AD 30-70 Christians orally inherited and passed down (i.e. popularized) storied reports about Jesus’s ministry. This page analyzes 7 evidences:
This provides a reason to think the Jerusalem passed-down Jesus biography to others because they were Christians par excellence.
The Jerusalem church put significant effort into passing down the stories/reports of Jesus which circulated among them, and they strove to relay them faithfully.
See this page to evaluate four supporting arguments:
If the Jerusalem church did really put effort into disseminating their Jesus-traditions to Christians throughout the Mediterranean (and the world), then it increases the probability that that they in fact did pass it down, i.e. that they accomplished what they set out to do.